I am primarly a koi keeper and not so much into watergarden like I used to be, but I do still have a stream. One of my koi ponds used to be my water lily pond. It spills into an 800 gallon pool, then into a stream, and finally into another 800 gallon pool before heading off to the filter. The biggest problem I had was keeping that stream clean from the decaying mulm and fish waste. Streams do a great job filtering, but I firmly believe that a filter system must be kept clean, including the stream. So last year, I made a couple of modifications to the stream that allow me to keep it clean.

The stream has several small waterfalls in it. I installed a 3" pipe under each waterfall area, and capped each pipe with a black rubber fernco cap. Then at the end of the stream, I installed a 3" pipe that ran underground to behind my ponds, so I could flush the stream and drain the waste away. That pipe has a cap on it as well. So now all I have to do is remove 4 rubber caps and wash all the gunk away! None of the gunk flows into the pool at the bottom of the stream anymore. Cleaning the stream used to be job that I dreaded, and now I don't. It's very easy and fast and because it is kept clean, it can do a better job with filtration.

Chas, I think what has happened is that your pond has reached a state where the filtration and the plant action is keeping the nutrients in check and the water chemistry is balanced. With that balanced state nothing is left for the algae to feed on.
Watercress roots are a great filtering system and the plant it's self thrives as it eats up excess nutrients in the water. This is especially so, if it is grown in the running water of a stream or in the rocks of a waterfall.
You have witnessed the filtration of the root system in action when you pulled the plant up out of the water. That mass of roots snares everything that tries to pass by.

Your whole stream bed is an oxygenating bio-filter, as is the sides of the pond, where the short fuzzy algae clings to it.
There is nothing better than natural filtration.
"Horton"

Does that mean your stream is flowing 24/7? How does that affect the evaporation rate of the water? And the electricity consumption?

In my case, electricity use is the same with the stream or without. If I had no stream, the water would simply get pumped back to the pond after filtration. With the stream, it is still pumped back to the pond from the pool at the bottom of the stream. To use a stream as part of your filtration, it must run 24/7 to keep the beneficial bacteria alive. You will get more evaporation with a stream, but you also get some good oxygenation in the water as it tumbles down the stream. I keep my stream running in the winter also, but I do pull a sheet of greenhouse film over it so it won't cool the pond off too much.

Would love to see pics of your stream. :) Do you think reducing the load of organic debris (by not feeding your fish) is the main cause of the decrease in algae? Also by repairing your leak you may have decreased whatever nutrients may have been in the source water you replenished the pond with? Just some of my guesses from ponding. Every system is different and glad to hear yours is working for you. I am sure the birds and local critters love to have a stream to get a refreshing drink from.

Lisa

Thanks for fast responses. Annaca, the stream runs 24/7/365, except for 3 weeks last winter when the hose blew off the pump while it was unseen under ice. The pond therefore completely sealed over. I was impressed that the fish survived anyway although that is probably not news to you northerners. I have a Laguna 2400gph that claims to only be 100 watts. I have not verified the wattage though I probably could and should check it. I suspect that I may still have a little waterfall spillage because I am losing an inch every 3 days or so. When i was diagnosing leak sources and diverted water from the filter AND the top two feet of the stream, I found almost no losses in several days (perhaps 1/4 inch)

Horton, I was hoping you would say something like your response.

goodkarma et. al. I would love to show pics. One of these days I will learn to set up a Fliker or whatever account. I see your point about water addition/nutrients. I am on a well but I also have an extra pond that I call my resevette that collects roof and french drain runoff instead of using rain barrels. It is mainly for irrigation but I often top off with the resevette water. It sometimes has suspended mud etc. Although it looks tolerable coming out of the hose, it looks pretty brown sitting in the resevette. It doesn't seem to even temporarily cloud up the pond which again says good things about the stream where I add the topoff water. But it sure could add extra nutrients and while I was diagnosing I didn't need as much water and I think I was mainly using the well anyway.

ccoombs, I like your cleaning design. Im lazy and haven't tried to clean the pond bottom. I have blasted hose water or even the power washer into the stream to clean that and again it cleans up in 15 minutes or so.